1. Field of the Invention
The present invention relates to infrared (IR) absorbing compositions and laminates. The compositions are in sheet form and contain lanthanum hexaboride (LaB6) dispersed in a thermoplastic polymeric matrix, together with other light attenuating components such as, without limitation, indium tin oxide, antimony tin oxide, organic dyes, and pigments.
The laminates are multilayer structures having at least one polymeric interlayer with LaB6 dispersed therein or coated thereon, alone or with other light absorbing components, and at least one additional interlayer such as an encapsulating layer, a dyed or pigmented layer, and/or a reflective layer.
2. Related Background Art
Polyvinyl butyral (PVB) resin sheet is used in light-transmitting laminates containing one or more rigid layers, such as glass, for applications such as automotive and architectural glazings, show cases, and protective glass for pictures, documents and the like. The PVB sheet absorbs energy and prevents disintegration when, for example, the head of a vehicle occupant strikes the rigid layer of a laminated window after a sudden stop or a foreign object is propelled against the outside of the laminate.
Glazings, including laminated glazings, tend to transmit heat energy. This can be particularly problematic in a confined area, such a vehicle passenger compartment or office, because of potential overheating of the confined area. Thus many techniques have been developed in an attempt to control heat transmission through glazings.
A conventional heat shielding transparent composite may comprise a very thin layer of reflective metal such as aluminum or silver which is deposited on a transparent substrate by vacuum deposition or sputtering techniques. This technique is limited on vehicle and building windows because the film thickness must be extremely thin. In addition, metallic layers may also suffer from corrosion problems.
It is known that nanoparticles of various inorganic oxides, can be dispersed within a resin binder to form coatings that absorb particular wavelength bands of infrared energy and allow high levels of transmission of visible light. In particular, U.S. Pat. No. 5,807,511 discloses that antimony doped tin oxide (ATO) has a very low transmission to infrared light having wavelength exceeding 1400 nm. U.S. Pat. No. 5,518,810 describes coatings containing tin doped indium oxide (ITO) particles that substantially block infrared light having wavelength above 1000 nm, and that the crystal structure of ITO can be modified to block light having wavelengths of down to 700-900 nm.
U.S. Pat. No. 5,830,568 describes a laminated glass with an interlayer film containing functional ultra-fine particles that provide heat insulation, ultraviolet ray absorption and maintenance of sufficient radio transmittance. The preferred interlayer film is polyvinyl butyral or ethylene-vinyl acetate copolymer. The exemplified ultra-fine particles include antimony tin oxide and indium tin oxide.
EP-A-1008564 discloses the use of an infrared blocking coating composition which contains both ATO or ITO, and metal hexaboride such as LaB6. The ATO or ITO blocks the higher wavelengths of infrared light and the metal hexaboride particles block the lower wavelengths of light. The coating may be applied to polymeric film substrates. There is no disclosure or suggestion, however, of employing metal hexaboride as a nanoparticulate dispersion in a PVB composition, particularly for use as an interlayer sheet in a glass laminate.